It is well known that the audible frequency range of an audio noise that can be heard by human ear is 20 Hz˜20 kHZ. In a switching converter, if the switching frequency of the switching converter decreases below 20 kHZ, audio noise will be generated. Thus, how to avoid the audio noise should be considered during the design of the switching converter. Generally, the switching frequency of the switching converter is much higher than 20 kHZ during a normal operation condition. However, when the switching converter operates in a light-load or no-load condition, the switching frequency of the switching converter may be lower than 20 kHZ which may result in occurrence of the audio noise.
Therefore, it is desired to have a solution for avoiding audio noise especially when the switching converter operates in the light-load or no-load condition.